Potentiometers



Dec- 15 1964 M. E. BOURNS ETAL 3,161,849

POTENTIOMETERS Filed Oct. 3C, 1961 United States Patent O 3,161,849FUIENIIGMEIERS Marian E. Bourne, 2536 Piedmont Drive, Riverside, Calif.;Marvin E. Harrison., 9M Thatcher Drive, Los Altos, Calif.; Wilbur 'I`.Hardison, 492@ Luther St., Riverside, Calif.; Bonald I.. Gas, 3951 HeidiRoad, Riverside, Calif.; and George F. Kuli, 4343 Bandini Ave.,Riverside, (Ialii.

Filed Get.. 3th, 196i, Ser. No. IMAGE 3i) Claims. (Cl. 333--IS3) Thisinvention relates to new and improved potentiomn eters.

This application is a continuation-impart of application Serial No.17,099 filed March 23, 1960, now abandoned, which application Serial No.17,099 is a division of application Serial No. 585,647 tiled May 18,1956, for potentiorneters.

For many years the principal requirements for electrical instrumentssuch as potentiometers have involved the accuracy of these instruments,the cost and the ease of their manufacture, and their ability towithstand physical abuse such as rough handling. At the present timepotentiometersV and other similar electrical instruments are employed invirtually all climates and at extremes of high temperature. Further,they are utilized in many applica tions, such as, for example, in guidedmissiles where the size of these instruments is an extremely materialconsideration. This widespread use of electrical instruments has ineffect relegated the cost and ease of assembly of many electricalinstruments to matters of secondary importance. The prime objective ofmany manufacturers is now to provide extremely small, light weightinstruments capable of withstanding virtually anything apparentlyirrespective yof the cost involved, even though cost and ease ofmanufacture remain important considerations.

One object of the present invention is to provide a potentiometercapable of being used under extremes of atmospheric or temperatureconditions, with retention o accuracy and reliability. Another basicobjective of the present invention is to teach the construction ofelectrical instruments of this category which are of extremely smallsize and weight. A further basic objective of the invention is toprovide potentiometers which are accurate and reliable, and which areextremely resistant to physical abuse. Still further objectives of thisinvention as Well as many advantages thereor` will be more fullyapparent to those skilled in the art to which the invention pertainsfrom the consideration of the remainder ol this specication, theappended claims and the accompanying drawing in which:

FIGURE l. is a perspective view of a potentiometer of the presentinvention;

FIGURE 2 is a cross sectional View taken at line 2-2 of FIGURE l;

FIGURE 3 is a cross sectional view taken at line 3-3 of FIGURE 2;

FIGURE 4 is a cross sectional view taken at line li-4 of FIGURE 2;

FIGURE 5 is a cross sectional View taken at line 5 5 of FIGURE 2;

FIGURE 6 is a partialcross sectional view similar to FIGURE 2, with aportion removed, showing a modilied form of the invention.

FIGURE 7 is a `cross sectional View taken at line 7 7 of FIGURE 6;

FIGURE 8 is a perspective view showing a terminal clip employed at theends of the resistance elements of the forms of the invention shown inthe preceding ligures;

FIGURE 9 is a view similar to FIGURE 2 of a second modifiedpotentiometer of the invention;

FIGURE 10 is a cross sectional View taken at line lili-Iii of FIGURE 9;

assista Patented Dec. I5, 1964 FIGURE ll is a cross sectional viewsimilar to FIG- URE 2 ot a third modified potentiometer ot theinvention; and

FIGURE l2 is a cross sectional view taken at line .i2-I2 of FIGURE ll.

Whenever convenient for purposes of illustration and explanation thesame or substantially the same parts of the different potentiometersillustrated are designated by identical numerals. It is to be understoodthat the accompanying drawing is not to be taken as limiting theinvention in any respect inasmuch as the sizes, shapes, and relativepositions of certain of the parts shown may be altered in a variety ofdierent ways without departing from the essential nature of thisinvention. In order that the invention may be more fully cornprehendedthe potentiometer shown in FIGURE 1 is drawn approximately to scalerepresenting an actual potentiometer built in accordance with thisdisclosure and having a width of approximately Ms and a height ofapproximately 3A6 and a length of approximately 3A".

As an aid to understanding the invention it may be stated in essentiallysummary form that it concerns potentiometers manufactured so as to haveterminal leads hermetically sealed to a non-conductive member and so asto have a housing sealed to this non-conductive member so as to denne anenvelope within which there are located a resistance element, meansserving as an electrical return, contact means connecting the electricalreturn and the resistance element, and means for moving the contactmeans. Obviously any summary of this category is essentially cursory innature, and hence is not to be taken as limiting the invention in anyrespect.

In order to completely understand this invention it is necessary torefer to the various figures of the drawing illustrating it. In FIGURESl, 2 and 3 there is shown a potentiometer Iii according to the presentinventionk built so as to include an elongate generally oval-shapedstrong metal housing I2 preferably of tubularform so as to avoid anywaste space within an envelope Id or cavity containing a resistanceelement I6 and a threaded metal shaft I8. n

The resistance element I6 is formed so as to extend in a straight pathgenerally parallel with the axis of a conductive metal wire 2t? servingas a support and as an electrical element. Around the periphery of thiswire 2@ there is located, as shown in FIGURE 5, a comparatively4 thinlayer 22 of a non-conductive material suchas, for example, a resinouslacquer or a ceramic-resin composition of a category known to the art.Located around this layer 22 is a continuous winding 24 of aresistancewire which preferably is secured to the layer 22 as thro-ughthe use of a composition serving as an adhesive. Such a material servingto hold the winding 24 in position can, if desired, be omitted.

Adjacent to and within the front end of the housing 12 there is locateda non-conductive support 28 formed of a ceramic or equivalent material,having openings 3i) and 372 therein. Over the end yof the resistanceyelement I6 adjacent to this support 23 there is positioned a clip 34,the construction of which is best seen in FIGURE 8 of the drawing. Thisclip includes a central washer-like section 36 designed to bear againstan end of the layer 22. It also includes three resilient arms 33 eachhaving `a bowed end 4@ designed to engage a portion of thev winding 24.It is considered obvious that all of these bowed ends itl engage thewinding 2d in the same plane transverse to the axis of the wire 2t?, Ifdesired they may be weldedto this winding or otherwise secured to it.From the center of the section 3e there project two convergingextensions 42 both having a curved 'interior configuration so that whenthe clip 3d is placed in an operative position these extensions engagean end of the wire 20 in a secure manner. If desired they may be Weldedor otherwise attached to this wire. The extensions 42 and the end of thewire 22 are preferably forced into the opening 30 as shown in FIGURE 2of the drawing so as to securely hold one end of the resistance element16 in position.

The other end of the resistance element 16 is held in place in part by aportion of the Wire 2t) projecting through a ceramic end 44. Anotherclip t6 having a cylindrical collar or ferrule 4S is located around thelayer 22 adjacent to this end 44 so that arms 50 similar to the arms 3Sprojecting from it are located with bowed ends 52 similar to the ends4t) engaging the winding 24 in substantially the manner previouslydescribed. These ends 52 may be welded or otherwise secured to thewinding 24- and the collar i8 may be attached to the layer 22 as by theuse of adhesive. Another wire S41 is welded or otherwise electricallyand physically attached to the collar 43 so as to project out throughthe end 44.

The wires 2i) and 54 are preferably united or bonded to the end 44 byany of various expedients known to the art so as to, in effect, behermetically sealed to this end 44. A third wire 56 is similarlypositioned so as to project into the envelope 14. This third wire isattached to a small metallic bearing 58 by being welded or otherwiseattached within a closely fitting hole di) in this bearing. Forming apart of the bearing S is a flangelike collar 62 having a slot 64 formedin one side thereof parallel to the axis of this bearing.

This structure is designed so that a generally cylindrical extension 6dof a shaft 63 can tit within the collar 62 in such a manner that it isheld by essentially spring tension as the shaft 18 is turned so that anelectric current can flow from the wire 56 to the shaft 15.8. A

threaded section 70 is formed upon shaft 13 for the purpose of holdingand moving a metal contact member 72. This contact member servesessentially as both a movable element or slider and as a contact memberhaving resilient ends 74 engaging the sides of the resistance winding24. The ends 74 are connected by means of a coiled section '76resembling a common coil spring. The individual turns of this section'76 are, as indicated in FiGURE 2, designed so as to fit in the grooveof the thread of the threaded section 7d; it preferably is of suchdimension that the threaded section 75B is engaged by essentially springtension so as to facilitate electrical contact; the pitch of the coiledsection "iti is preferably different from the section 7d for the samepurpose.

The end of the shaft 68 adjacent to the front end 26 is provided with acollar 78 which normally rests against the support 2d so that the shaftitself can project through the opening 32. On the side of the support 28remote from the envelope lll a flat, non-round head St? is formed onthis shaft 68.

As is best seen in FIGURE 2 of the drawings, the housing 12 ismanufactured so as to include an end $2 against which the support 23rests. Further, this end 82 includes Va collar 8dprojecting therefromaround the head 80; upon the end of this collar there is provided `asmall outwardly extending flange Sd. A metal cap 88 is positioned sothat an inwardly extending tiange 9d on it resiliently engages `theliange 6 forming a rotary seal. The cap 8S is held in this sealedposition by means of an elastomeric retainer @2 of rubber or othersimilar material. As illustrated this retainer 92 completely engages thehead Sti so thatV as a slot 94 in the cap 83 is actuated by means of ascrew driver or the like the shaft 18 is caused to rotate.V

It is preferred to form the potentiometer fd with a small metal band 96located around and sealed to the end 44 so that this band maybe directlywelded or soldered Vto the housing l2 during assembly. lt is consideredto be obvious from the drawing that the contact member 72 is preferablyformed out of a conductive metal wire having substantially circularcross section. Also, the clips 34 and d6 are preferably formed out of aresilient conductive metal. If desired, the envelope id may beevacuated, or may be lled with any desired gas such as, for example, aninert gas incapable of causing corrosion even when the potentiometer l0is to be operated at an elevated temperature.

It will be realized from the foregoing description that potentiometer l@is a very compact, efficient device. Units constructed as shown may beoperated under humidity extremes such as are found in the tropicswithout significant danger of damage caused by fungus growth within theenvelope 14 or the like. Further, they may be Operated where they may besubjected to extremely rapid temperature cycling. In addition, unitsconstructed to be like or similar to potentiometer 10 are resistant tohandling damage and other physical abuse, are accurate, and arecomparatively easy to assemble and manufacture. Many of thesecharacteristics are, at least in part, a result of the specific sealsused to seal the envelope 14. Specific attention is directed to thestructure of the retainer 92 and to the fact that this retainer is, ineffect, distorted by the collar 34, effecting a seal in addition to thatobtained between the anges S6 and 90.

In FGURE 6 of the drawing there is shown a modified potentiometer litt)which is structurally similar to the potentiometer ld except for severaiminor differences. One of these differences is that the resistanceelement Sie shown in FlGURES 6 :and 7 does not utilize a winding such asthe winding 24 but instead employs a very thin resistance film 162, suchas, for example, a pyrolytic boro-carbon film, a metal resistance film,or the like. By virtue of the sealed nature of the potentiometer 100,lms which are apt to change resistance characteristics in conventionalpotentiometers where the resistance element is open to the atmospherecan be satisfactorily employed with this invention. Obviously either ofthe resistance elements 16 or f6 can be interchanged with the other.

The potentiometer Miti also differs from the previously described unitin that a support 28 is employed which is only half the size ofpreviously mentioned support 23. With this construction the opening 32is replaced in the same general area by a head embedded in anelastomeric retainer 92. Portions of the retainer 92 within the housingl2 are compressed by an inwardly turned collar 3d so as tol form anefficient seal. A cap 88', as previously indicated, is held by theretainer 92. If desired, a plurality of annular ridges 104i can beformed within the coliar 3d upon the retainer' 92 so as to aid inestablishing effective sealing `at several locations. The collar Sd inthe potentiometer fritti also serves to compress the retainer 92 so asto iirmly hold the shaft 68 in position.

In FIGURES 9 and l0 of the drawing there is Shown a modied form orembodiment of potentiometer liti according to the invention, whichembodiment includes an elongated ceramic base M2 through which there arepassed portions of wires lfd and 116. These wires are fused to the base'1112, with the preferred construction of this embodiment of thisinvention being substantially as previously indicated. The wire fteextends along the surface of thc base :lf2 Within an envelope M8 and isprovided with a bent over end which may be fused directly to the base soas to securely hold the wire i116 against movement. Theentire wire lillemay, Vif desired, have the part of its surface that is disposed withinthis envelope fused to the base i12, or may be attached to it by meansof an appropriate adhesive. If either of the latter are done it ispossible to omit the end 12d.

The other wires lid are attached as by welding or the like to the endsof a resistance element 122 which may be of conventional construction insuch a manner as to hold this element upon the surface of the base 112within the envelope 118. lf desired the resistance element 122 may alsobe in part fused to the base 112 or may be secured thereto by the use ofan adhesive. Hermetically sealed to the sides of the base 112 is a metalcover 124 which may, if desired, be termed a housing. It is consideredobvious that this cover defines the complete envelope 118 in conjunctionwith the base 112. Supported upon cover 124 Within the envelope 118 is asmall bracket 126 having an end opening (not shown) formed therein. Anopening 128 aligned with the opening in bracket 126 is provided in thecover 124. These two openings serve to hold cylindrical extensions 13@of reduced diameter extending from the ends of a threaded section 132 ofa shaft 134. This shaft is, as indicated, parallel to both theresistance element 122 and the adjacent part of wire 116. Smallelastomeric O-rings 136 are positioned around the cylindrical extension138 projecting through the opening 128. A cap 138 having a slot Mtlformed therein is Aattached as by welding or the like to this extension13@ so as to hold the O-rings 136 constantly under compression forming adouble seal.

When the shaft 134 is turned the opening in the bracket 126 and theopening 128 serve essentially as bearings supporting this shaft so that`a Contact member 142 is moved with respect to the resistance element122 and the wire 116. This wire serves as an electrical return in thestructure shown. The contact member 142 is preferably formed similar tothe contact member 72 out of a resilient wire so as to include aspring-like coiled section 144 similar to the coiled section 7d engagingthe threads on the threaded section 132 of the shaft 134. Ends 146 ofthe contact member 142 lead from the coiled section 144 as indicated inFIGURE 1G of the drawing so as to resiliently engage the wire 116 andthe furthest removed side of the resistance element 122. By virtue ofthe configurations and relative dispositions of the ends 146 thiscontact member engages portions of the resistance element 122 and thewire 116 so `as to be incapable of turning as the shaft 132 is rotated.

In FIGURES l1 and 12 there is illustrated a third i modified form ofpotentiometer, indicated generally by ordinal 150, according to thepresent invention, which employs a non-conductive ceramic base member 12to the ends of which there is attached a generally U-shaped, rigid,non-conductive yoke 154. This yoke may be attached to the base 152 bymeans of an adhesive or any other equivalent means known to the art. Itis covered by means such as a metal cover or housing 156 which issecured to the base 152 in substantially the same manner in which thehousing 12 is secured to the end 44 in the potentiometer 1t). A wire 158corresponding to the wire 2t) passes through the base 152 and thence tothe extremity of the yoke 154 remote from the base where it passesthrough an opening 168, and then is bent so as to pass through anotheropening 162. The end of this wire 158 is secured as by welding or thelike to a resistance winding 164 positioned around a non-conductivelayer 166.

The construction of the resistance winding 164, the layer 166 and thewire 158 corresponds to the construction of the resistance element 16and will not be described in detail. The end of the resistance winding164 adjacent to the base 152 is attached to another wire 168 as bywelding; this other wire also passes through the base 152. A third wire170 passes through the base 152 and through an opening 172 in the yoke154 in such a manner as to be supported against movement by this yoke.The wires 158, 163, and 170 are all sealed with respect to the base 152in the manner previously indicated.

Within the base 1552 there is provided an opening 17dwhich is surroundedby a circular depression 17d within which there is located a commonO-ring 178 formed of an elastomeric material. A head 180 having a slot182 formed therein is positioned against this D-ring so as to normallydeform it forming a seal; a short, round shaft section 184 extends fromthe head 180 through the O-ring 178 and through the opening 174 where itis supported in Such a manner that it may be readily rotated. A nonroundshaft section 186 extends from the round shaft 184 to be immediatelyadjacent to an opening 188 in the yoke 154. There a small, round shaftsection 190 is provided so as to extend from the non-round section 186through this opening 188 in order for the opening to serve essentiallyas a bearing. A head 192 is provided on the end of the section 1% so asto bear against the yoke 154 holding the head 188 firmly in position atall times.

Around the non-round shaft section 186 there is provided a cylindrical,non-conductive, externally-threaded sleeve 194 having an opening 196 inthe center thereof corresponding in shape and dimension to the non-roundshaft section 186. A contact member 198 having the configuration bestshown in FIGURE l2 of the drawings is snapped into place around thesleeve 194 so that threads (not shown) on the center section 209 of thiscontact member engage the threads on the exterior of the sleeve 19d.Bowed, curved extensions 282 from the sides of the center section 2410resiliently engage the sides of the wire and the resistance winding 164so as to establish electrical communication between these two parts. Byvirtue of this construction the contact member 198 is very easy toassemble and is capable of riding up on the threads on the sleeve 19311when the shaft construction shown has been turned too far in eitherdirection, so as to prevent damage. This contact member 198 may beconveniently formed by simple metal stamping operations. By virtue ofthe fact that it is bowed where it engages the resistance element andthe eiectrieal return so as to, in effect, establish point contact alonga line through its center on both sides of these two members there islittle danger of it catching so as to prevent uniform movement duringthe operation of the potentiometer 150.

The difference in the operation of the contact member 198 and thecontact members 72 and 142 should be specifically noted. The contactmember 198 tends to spring apart so as to override the threads uponwhich it is normally carried when adjusted to either end of thepotentiometer 158. As opposed to this the Contact member 72 in thepotentiometer 1@ is threaded off of the ends of the shaft 18 and iscompressed against either of the adjacent members in this unit whenmoved to either end of the unit. Thereiu the Contact member 72compresses essentially as a coil spring. When the direction of theshafts rotation is reversed this contact member 72 reverses itself and,by virtue of the compression within it, rethreads itself upon the shaft18. The contact member 142 can be formed so as to operate in a similarmanner; It is also possible to utilize this contact member so that theturns of the coiled section 14ml spread apart overriding the threadsupon the shaft, although this is not generally preferred. Both of thesemethods of operation of contact members are considered to beadvantageous; with either of these methods damage resulting from turningthe shaft too far is prevented. The previous description of contactmember 72, for example, makes evident the fact that the Contact memberis inherently resilient and has spacedapart convolutions or elementsthat engage the screwthreaded shaft (such as shaft 18) at longitudinallyspacedapart locations and around at least substantially the entireperiphery of the shaft thereat. The convolutions or elements arecollectively and individually resilient and are thus adapted toindividually or collectively'disengage from the thread of the shaft inthe manners hereinbefore explained. Further, in the case of either typeof disengagement, the member is so constructed and arranged that due tostressing of one or more of the elements of the coiled part of themember automatically re-engages with the thread of the shaft incident toreverse rotation of the shaft. During the limited rotation of the shaftsasha-ss M ef the contact member (either '72 or 142) is traversedlongitudinally along the shaft and thus its contact is traversed alongand in contact with a portion of the resistance element. The housing andsupport means (such as 14, 44, 28, etc.) which house and support theresistance element and screw-threaded shaft are so constructed andarranged as to limit traversing movement of the contact member to `thateffected during only a limited rotation of the shaft; and further orexcessive rotation of the shaft results in yielding of one or more ofthe convolutions or elements of the contact member (radially in the caseof a shaft such as 134 and longitudinally in the case of a shaft such as18) so that jamming and damage to parts of the resistor are avoided. Asnoted, subsequent reverse rotation of the shaft permits the convolutionsor elements of the contact member to re-engage the thread of the screw,that action being automatic due to the stress in the resilientconvolutions of the contact member. lt further is evident that ascrew-threaded shaft of the type illustrated in FIG. 2 (shaft 13) may beemployed with a contact member such as member 114 (FIG. 9); and that theshaft depicted in FIG. 9 could be moditied in the manner suggested byFIG. 2, that is, could be provided with non-threaded end-portions ontowhich the contact member is traversed at either end of its travel.

The construction of the potentiometer l() is considered to beparticularly advantageous for many purposes since all of the operativeelements of this instrument can be assembled and tested for properfunctioning prior to the attachment of the cover lSo to the base 152.Such attachment is preferably by various means effecting a hermetic sealsuch as are employed with the potentiometers 1t) and 110. Obviously thistype of construction employing a yoke or support may be employed with aconductive shaft, omitting the wire lti serving as an electrical return.In this case, one of the bends in the contact member 19S can be omitted.

In describing the potentiometers titl, Mtl and reference has been madeto the ceramic end 44, the ceramic base M2, and the ceramic base i152.The term ceramic used here is used in its broadest possible sense so asto cover any fused oxide composition of an impermeable nature. Thus,this term covers various ceramic compositions of a category known to theart as well as various glass compositions that are, according to a fewreferences, classified as ceramic. Such glass compositions are on manyoccasions not classitied as ceramic. This explanatory notation isinserted herein in order to prevent any confusion as to the meaning ofthe terms employed. For the end 44 and the bases M2; and 1512 it ispossible to substitute other non-conductive materials having propertiessimilar to those of ceramics, which materials can be used for a hermeticseal. As an example of this, certain epoxy resin compositions and thelike can be utilized, although inorganic materials are preferred becauseof their physical and other properties.

It is to be noted that all of the instruments herein described can beconsidered to be, in effect, hermetically sealed, although in actualitya true hermetic seal is not employed where a shaft is connected to theoutside of the units in this invention. The shaft seals are, however, ofa construction and arrangement suiicient to withstand moisturepenetration, physical shoclr, etc., and the various shaft seals shownare in many respects the equivalent of a true hermetic seal. The truehermetic seals used to seal the other parts of the vinstruments of thisinvention so as to form an envelope are very advantageous as previouslyindicated.

Those skilled in the art to which this invention pertains Awill realizethat all of the constructions shown have the basic advantageouscharacteristics found in the potentiometer lil, although With variationin degree in certain cases. Many of the individual features shown hereinare applicable toother than what may be consid-credito be hermeticallyscaled units. VThus, for example, any

of the contact members described can be used with potentiometers of amore conventional construction, even though in certain cases minorvariations in structure may be required. Since the structures shown canbe varied without departing from the essential nature of this invention,and since many of the features of these structures have separateutility, this invention is to be considered as being limited only by theappended claims.

We claim:

1. in a potentiometer of the type having a housing defining a cavitywherein there is an elongated resistance element, a rotatably supportedthreaded shaft, a contact element slidahly engaging said elongatedresistance element and carried by said threaded shaft to be moved alongsaid resistance element with rotation of said shaft, and terminal meansatiording external connections with said elongated resistance elementand said contact element, the improvement comprising means forming wallsincluding an end wall having therein an opening, said shaft beingdisposed principally in said cavity and with one end thereof extendinginto the opening defined by said end Wall, an elastomeric ring extendingthrough said opening and disposed in part in said cavity and in partoutside thereof and having end dimensions larger than the opening and atsaid opening being of a diameter suliciently large to 'oe undercompression by said end wall at said opening and constructed andarranged to hold said one end of said threaded shaft which extends intosaid elastomeric material ring.

2. ln a potentiometer as recited in claim 1 wherein said wall having anopening is bent to form a collar delining said opening in which saidelastomeric retaining ring is held in compression.

3. ln a potentiometer as recited in claim 2 wherein said ring has aplurality of annular ridges within said collar for establishing a sealat a plurality of locations at said opening.

4. A variable resistor, comprising, in combination: a nonconductive basemember, a resistance element positioned on said nonconductive member,two terminal means for said resistance element extending therefromthrough said nonconductive base member and said terminal means beingsealed to said nonconductive base member; an electrical return wireextending along and sealed to said nonconductive base member anddisposed parallel to said resistance element and having a terminal, saidelectrical return wire terminal extending through and being sealed tosaid nonconductive 1oase member, housing means sealed to saidnonconductive base mem- `er so as to define a sealed envelope containingsaid resistance element and said electrical return Wire, said housingmeans having an opening therein, a shaft extending into said housingthrough said opening and arranged generally parallel to said resistanceelement; resilient contact means carried by said shaft within saidenvelope, said lcontact means engaging said resistance element and saidelectrical return wire so as to establish electrical communicationtherebetween; and means sealing said opening around said shaft toprevent passage of foreign matter into said envelope.

5. A variable resistor as defined in claim 4, wherein said resilientcontact means is formed of a single piece of material having ahelicallycoiled portion resiliently engaging said shaft and having endsresiliently engaging respective ones of said electrical return wire andsaid resistance element so as to establish electrical communicationtherebetween and effective to prevent rotation of said contact means.

6. ln a potentiometer of the type having an elongated resistanceelement, an electrical return conductor coextensive with spaced, fromand parallel to said elongated resistance element, a rotatably supportedthreaded shaft, an improved contact element comprising a resilient flatstrip .having a central portion Wound around` said threaded shaft to bein operative engagement with the thread thereof and movable along saidthreaded shaft with rotation thereof, and having one end extending toslidably engage said elongated resistance eiement and the other endextending to slidably engage said electrical return conductor.

7. A variable resistor comprising, in combination: a nonconductivemember having an opening formed therein; a yoke-shaped nonconductivesupport member attached at its ends to said nonconductive member so asto extend therefrom; a housing sealed to said nonconductive member so asto extend over said support member, said housing defining in conjunctionwith said nonconduotive member an envelope; an electrical resistanceelement positioned within said envelope so as to extend between saidnonconductive member and said support member; an electrical returnpositioned so as to extend within said envelope between saidnonconductive member and said support member; a shaft positioned so asto extend through said opening into said envelope, an extremity of saidshaft being supported by said support member; a contact member includingresilient electrically conductive means engaging said resistance elementand said electrical return, said contact member being carried by saidshaft within said envelope; and terminal means for the ends of saidresistance element, and other terminal means for said electrical returnall passing through and seated to said nonconductive member.

8. An electrical instrument as defined in claim 7 Wherein saidelectrical return and one of said terminal means are formed of a singlepiece of wire.

9. An electrical instrument as defined in claim 7 Wherein said shaftincludes a nonround portion located Within said envelope and wherein anonconductive sleeve having a threaded exterior and a nonround interiorcorresponding tothe shape of said nonround portion is positioned aroundsaid nonround portion and wherein said contact member is formed of asingle piece of resilient conductive metal so as to include a centersection which is positioned so as to engage the threads on said sleeveand so as to include ends engaging the sides of said electrical returnand the sides of said resistance element.

10. An electrical instrument as defined in claim 9 wherein one of saidterminal means comprises a wire extending from said nonconductive memberto said support member and wherein said resistance element includes anonconductive layer deposited upon all but extending ends of saidextending wire and a resistance winding positioned upon saidnonconductive layer, one end of said extending wire ends being bentaround to contact said resistance wire at one end.

ll. In a potentiometer of the type having an elongated resistanceelement, a rotatably supported threaded shaft spaced therefrom and anelectrical return conductor between and aligned with said threadedshafty and said elongated resistance element, an improved contact devicecomprising a resilient wire having end portions and a central portionsubstantially encircling said threaded shaft and operatively engagedwith the thread of the shaft, said resilient member having legsextending from either side of said central portion, the end of one ofsaid legs being constructed and arranged to engage said elongatedresistance element, and a portion of said legs between the ends and thecentral portion being bent to slidably engage said electrical returnconductor.

l2. A variable resistor of the leadscrew actuated type, comprising, incombination:

first means, comprising an elongate resistance element and a conductiveleadscrew having first and second ends and said irst means including acontact device,

said first means being constructed and arranged for wiping movement ofthe contact device along the resistance element to effect variable.electrical interconnection of the resistance element and leadscrewincident to rotation of the latter;

second means, comprising insulative base means and electrical terminalmeans extending through and i@ sealed to said base means, a terminaldevice comprised in said terminal means being constructed and arrangedas a bearing to rotatably support the first end of said leadscrew andserving to conduct electrical current conducted by the leadscrew;

and third means, including support means for said resistance element andthe second end of said leadscrew and including housing means constructedand arranged to enclose said contact device and said resistance element,constructed and arranged for electricai and mechanical operation of thevariable resistor.

13. in a variable resistor of the leadscrew actuated type hav-ing anelongate resistance element and a contact device responsive to operationof a leadscrew to wipe along an extent of the resistance element, theimprovement comprising:

iirst means, including elongate housing means comprising insulative basemeans and casing means having a portion provid-ing a tubular openingcommunicating with the interior of the housing;

and second means, including bearing means and leadscrew meansoperatively engaging the contact device and rotatively mounted on thebearing means, said leadscrew means comprising a leadscrew having a headportion including an elastomeric member and a rigid body portionterminated by an end portion formed for rotative cooperation with theelastomeric member and engaged therewith, said elastomeric member beingdisposed in part in said tubular opening and constructed and arrangedfor rotation therein for rotating the body portion of the leadscrew andfor sealing said opening against passage of foreign material.

14. A variable resistor as defined in claim 13, including on saidelastomeric member a rigid cap means engaging the elastomer-ic memberfor rotation thereof, said cap means being constructed and arranged forcooperation with said casing means.

15. A variable resistor of the leadscrew-adjusted type, comprising:

iirst means, comprising an elongate resistance element,

and means including electrical connections to end portions of theresistance element;

second means, comprising housing and support means,

constructed and arranged for supporting said resistance element; thirdmeans, comprising an elongate screw-threaded shaft supported by saidsecond means in substantially parallel disposition relative to saidresistance element; and Y fourth means, comprising a contact devicehaving resilient portions yieldingly engaging said screwthreaded shaftaround a substantial portion of the periphery thereof atl at least twolongitudinally spaced-apart locations along the shaft for traverse ofthe device along the shaft incident to limited rotation of the shaft`and whereby the device may yield relative to the thread of the shaftand may discontinue traverse incident to excessive rotation of theshaft, said contact device comprising means for electrieally contactingsaid resistance element, whereby limited rotation of said shaft within arange of rotation thereof causes a change of resistancer to be exhibitedbetween said deviceand either of said end portions of said resistanceelement and whereby during'excessive rotation of said shaft said deviceslips relative to the shaft and does not cause "a change of resistanceto be exhibited as stated. 16. A variable resistor according to claiml5, said device and said shaft being both electrically conductive andsaid terminals including a terminal electrically connected to saidshaft.n

17.A variable resistor according to claim 16, said shaft having adriving end, and driving means including sadness l l insulation means inwhich said driving end is embedded whereby rotation of said shaft may beeffected by rotation of said insulation means.

18. A variable resistor according to claim l5, said screw threaded shaftcomprising a non-threaded portion at an end of the threaded portionthereof, upon which nonthreaded portion said device is forced incidentto continued rotation of said shaft.

19. A variable resistor according to claim 15, said contact devicecomprising a coil spring having a plurality of convolutions engaged withthe thread of said shaft.

20. A variable resistor comprising:

first means, comprising housing and support means;

second means, comprising an elongate resistance element housed andsupported by said first means, said second means comprising electricalterminal and connection means supported by said first means andproviding electrical connections to respective end portions of saidresistance element;

third means comprising a screw-threaded shaft housed and supported bysaid first means, said shaft being disposed substantially parallel tosaid resistance element; `and fourth means, comprising a contact devicehaving a helically coiled wire portion having the convolutions thereofengaged with the thread of said shaft for traverse therealong incidentto shaft rotation, and said device having `a contact bearing on saidresistance element for traverse therealong incident to traverse of saiddevice.

21. A potentiometer which comprises: a ceramic member; a metal housingsealed to said ceramic member so as to detine an envelope; threeelectric wires passing through said ceramic member, said wires beingsealed to said ceramic member and being insulated from one another, oneof said wires extending through said envelope; `a non-conductive coatingpositioned upon said wire extending through said envelope within saidenvelope; a resistance element positioned upon said nonconductivecoating; lmeans electrically connecting the ends of said resistanceelement with said wire extending through said envelope and with anotherof said wires; a conductive shaft positioned so as to extend throughsaid envelope, said shaft including a threaded portion within saidenvelope; means establishing electrical connection between said threadedshaftgand the third of said Wires; a contact member carried by saidthreaded portion of said shaft and engaging said resistance element,said contact member being electrically conductive; and means forrotating said shaft so as to move said contact member within saidhousing.

22. An electrical instrument which comprises: a first non-conductivemember; 'a metal housing sealed to said first non-conductive member soas to define an envelope; three electric Wires passing through said rstnon-conductive member, said wires being sealed to said lirstnonconductive member and being insulated from one another, one of saidwires extending through said envelope; a second non-conductive memberpositioned within said envelope so as to support the end of said wireextending through said envelope remote from said first non-conductivemember; a non-conductive coating positioned upon said wire extendingthrough said envelope within said envelope; a resistance elementpositioned upon said nonconductive coating; means electricallyconnecting the ends of said resistance element with said wire extendingthrough said envelope and Ianother of said wires; an electricallyconductive shaft positioned so as to extend through said envelope, saidshaft including a threaded portion withinsaid envelope; meansestablishing elec-v trical connection between said threaded shaft andthe third of said wires, said means being located within said envelope;a resilient metal contact member carried byV said threaded'portion ofsaid shaft land engaging said resistance element, said contact memberbeing capable l?. of being disengaged from the threaded portion of saidshaft when said shaft is turned so as to move said contact member beyondeither end of said threaded portion; and means projecting into saidenvelope for rotating said shaft.

23. An electrical instrument which comprises: a nonconductive member; ametal housing sealed to said nonconductive member so as to define anenvelope; three electric wires passing through said non-conductivemember, said wires being sealed to said non-conductive member and beinginsulated from one another, one of said wires extending through saidenvelope; a non-conductive member positioned Within said envelope so asto support the end of said wire extending through said envelope remotefrom said first non-conductive member; a non-conductive coatingpositioned upon said wire extending through said envelope within saidenvelope; a resistance element positioned upon said non-conductivecoating; means electrically connecting the ends of said resistanceelement with said wire extending through said envelope and another ofsaid wires; an electrically conductive shaft positioned so as to extendthrough said envelope, said shaft including a threaded portion withinsaid envelope; means establishing electrical connection between saidthreaded shaft and the third of said wires, said means being locatedwithin said envelope; a resilient metal contact member carried by saidthreaded portion of said shaft, said contact member being capable ofbeing disengaged from the threaded portion of said shaft when said shaftis turned so as to move said contact member beyond either end of saidthreaded portion, said contact member including resilient means engagingsaid resistance element so as to establish electrical contact therewithand so as to prevent rotation of said contact member when said shaft isrotated; and means projecting into said envelope for rotating saidshaft.

24. An electrical instrument which comprises: a nonconductive member; ametal housing sealed to said nonconductive member so as to define anenvelope; three electric wires passing through said non-conductivemember, said wires being sealed to said non-conductive member and beinginsulated from one another, one of said wires extending through saidenvelope; a non-conductive member positioned within said envelope so asto ysupport the end of said wire extending through said envelope remotefrom said first non-conductive member; a non-conductive coatingpositioned upon said wire extending through said envelope within saidenvelope; a resistance element positioned upon said non-conductivecoating; means electrica lly connecting the ends of said resistanceelement with saidV wire extending through said envelope and another ofsaid wires; an electrically conductive shaft positioned so as to extendthrough said envelope, said shaft including a threaded portion withinsaid envelope; means establishing electrical connection between saidthreaded shaft and the third of said wires, said means being locatedyWithin said envelope; a resilient metal contact member having a coiledcenter section and projecting ends, said contact member being positionedwithin said housing so that said coiled center section is normallyengaged by the vthreads on said shaft, said ends engaging saidresistance element in Va plane transverse to the axis of said Wirepassing through said envelope on both sides of saidresistance element soas to prevent rotation of said contact member when said shaft isrotated; and means projecting into said envelope for rotating saidshaft.

25. An electrical instrument Which'comprises: a nonconductive member; ametal housing sealed to said nonconductivemember so as to define anenvelope; three electric Wires passing through said non-conduetivemember, said wires-being sealed to said non-conductive member and beinginsulated from one another; an electrical resistance element positionedWithin said envelope so as to be .insulated from said housing; meansconnecting the ends of said resistance element with two of said wires;an

electrically conductive shaft positioned so as to extend through saidenvelope, said shaft being rotatably mounted and including a threadedportion and a cylindrical extension within said envelope; meanspositioned within said envelope and attached to the third of said wiresresiliently engaging said cylindrical extension so as to establishelectrical connection between said shaft and said third wire; aresilient metal contact member carried by the threaded portion of saidshaft, said contact member being capable of being disengaged from thethreaded portion of said shaft when said shaft is turned so as to movesaid contact member beyond either end of said threaded portion, saidcontact member including resilient means engaging said resistanceelement so as to establish electrical contact therewith and so as toprevent rotation of said contact member when said shaft is rotated; andmeans for rotating said shaft.

26. An electrical instrument which comprises: a nonconductive member; ametal housing sealed to said non conductive member so as to define anenvelope; three electric wires passing through said non-conductivemember, said wires being sealed to said non-conductive member and beinginsulated from one another; an electrical resistance element positionedWithin said envelope so as to be insulated from said housing; meansconnecting the ends of said resistance element with two of said wires;an electrically conductive shaft positioned so as to extend into saidenvelope, said shaft including a threaded portion and a cylindricalextension Within said envelope; bearing means resiliently holding saidcylindrical extension positioned within said envelope and attached tothe third of said Wires so as to establish electrical connection betweensaid shaft and said third Wire; a resilient metal contact member carriedby the threaded portion of said shaft, said contact member includingresilient means engaging said resistance element so as to establishelectrical communication therewith; and means for rotating said shaft.

27. An electrical instrument of the class described which includes:means defining a housing; an electrical resistance element positionedwithin said housing so as to be insulated therefrom; an electricallyconductive shaft positioned so as to extend into said housing, saidshaft being insulated from said housing and including a threaded portionand a cylindrical portion located Within said housing; bearing meansresiliently holding said cylindrical portion of said shaft, said bearingmeans being positioned within said housing and insulated therefrom;

CTI

a resilient metal contact member carried by said threaded portion ofsaid shaft, said contact member being capable of being disengaged fromsaid threaded portion of said shaft when said shaft is turned so as tomove said contact member beyond either end of said threaded portion,said Contact member including resilient means engaging the sides of saidresistance element so as to establish electrical contact therewith andso as to prevent rotation of said contact member when said shaft isrotated; and terminal means attached to the ends of said resistanceelement and to said bearing means, said terminal means being insulatedfrom one another and from said housing and extending -to the exterior ofsaid housing.

28. An electrical instrument as defined in claim 27 wherein saidresilient contact member includes a coiled section normally threaded onsaid threaded portion of said shaft and includes ends engaging sides ofsaid resistance element.

29. An electrical instrument as defined in claim 26, wherein said meansfor rotating said shaft comprises a non-conductive member attached toone end of said shaft and resiliently engaging said metal housing toform a seal therewith; and a metal shell enclosing said non-conductivemember, said metal shell being formed to receive an adjusting tool forrotating said shaft.

30. An electrical instrument as recited in claim 27 wherein said housinghas an opening at one end dened by an extension in the Walls of saidhousing, one end of said electrically conductive shaft extending intosaid opening, an elastomeric material ring filling said opening,extending beyond both sides of the extension of said housing Wallsdefining said opening and having a diameter sufficiently large to beunder compression by the extension of said housing walls and therebyhold said one end of said threaded shaft, a cap fitted over and engagingthe portion of said elastomeric material ring extending on the outsideof said housing walls, said cap being crimped over the extension of saidhousing walls and being formed to receive an adjusting tool for rotatingsaid elastomeric material ring and thereby said shaft.

References Cited in the file of this patent UNITED STATES PATENTS2,870,304 OBrain Jan. 20, 1959 2,873,338 Elliott Feb. 10, 1959 2,886,681Bourns et al. May l2, 1959 2,895,116 Morrison July 14, 1959

1. IN A POTENTIOMETER OF THE TYPE HAVING A HOUSING DEFINING A CAVITYWHEREIN THERE IS AN ELONGATED RESISTANCE ELEMENT, A ROTATABLY SUPPORTEDTHREADED SHAFT, A CONTACT ELEMENT SLIDABLY ENGAGING SAID ELONGATEDRESISTANCE ELEMENT AND CARRIED BY SAID THREADED SHAFT TO BE MOVED ALONGSAID RESISTANCE ELEMENT WITH ROTATION OF SAID SHAFT, AND TERMINAL MEANSAFFORDING EXTERNAL CONNECTIONS WITH SAID ELONGATED RESISTANCE ELEMENTAND SAID CONTACT ELEMENT, THE IMPROVEMENT COMPRISING MEANS FORMING WALLSINCLUDING AN END WALL HAVING THEREIN AN OPENING, SAID SHAFT BEINGDISPOSED PRINCIPALLY IN SAID CAVITY AND WITH ONE END THEREOF EXTENDINGINTO THE OPENING DEFINED BY SAID END WALL, AN ELASTOMERIC RING EXTENDINGTHROUGH SAID OPENING AND DISPOSED IN PART IN SAID CAVITY AND IN PARTOUTSIDE THEREOF AND HAVING END DIMENSIONS LARGER THAN THE OPENING AND ATSAID OPENING BEING OF A DIAMETER SUFFICIENTLY LARGE TO BE UNDERCOMPRESSION BY SAID END WALL AT SAID OPENING AND CONSTRUCTED ANDARRANGED TO HOLD SAID ONE END OF SAID THREADED SHAFT WHICH EXTENDS INTOSAID ELASTOMERIC MATERIAL RING.